Sequential Pore Functionalization in MOFs for Enhanced Carbon Dioxide Capture

The capture of carbon dioxide (CO₂) is crucial for reducing greenhouse emissions and achieving net-zero emission goals. Metal-organic frameworks (MOFs) present a promising solution for carbon capture due to their structural adaptability, tunability, porosity, and pore modification. In this research, we explored the use of a copper (Cu(II))-based MOF called <i>m</i> <b>CBMOF-1</b>. After activation, <i>m</i> <b>CBMOF-1</b> generates one-dimensional channels with square cross sections, featuring sets of four Cu(II) open metal sites spaced by 6.042 Å, allowing strong interactions with coordinating molecules. To investigate this capability, <i>m</i> <b>CBMOF-1</b> was exposed to ammonia (NH₃) gas, resulting in hysteretic NH₃ isotherms indicative of strong interactions between Cu(II) and NH₃. At 150 mbar and 298 K, the NH₃-loaded (∼1 mmol/g) material exhibited a 106% increase in CO₂ uptake compared to that of the pristine <i>m</i> <b>CBMOF-1</b>. Carbon-13 solid-state nuclear magnetic resonance spectra and density functional theory calculations confirmed that the sequential loading of NH₃ followed by CO₂ adsorption generated a copper-carbamic acid complex within the pores of <i>m</i> <b>CBMOF-1</b>. Our study highlights the effectiveness of sequential pore functionalization in MOFs as an attractive strategy for enhancing the interactions of MOFs with small molecules such as CO₂.